Several methods are known as radiation measurement methods using scintillators. A solid scintillator method is a method of measuring radiation using a solid scintillator (for example, a plastic scintillator). In general, with this method, it is difficult to measure low-energy radiation; that is, radiation with short maximum ranges (reaching distances). For example, a method may be considered in which a liquid drop of a liquid sample containing tritium is placed on a surface of a scintillator plate or the liquid drop is spread to form a liquid layer on the surface, and β-ray emitted from tritium is detected in this state. However, the maximum range of the β-ray emitted from tritium is only about 5 mm in the air, and about 6 μm in water. Therefore, the β-ray emitted from the tritium is significantly attenuated (self-absorption) during the process of passing through the liquid sample itself. Because of this, an amount of β-ray exiting from the liquid sample would be very small, and sufficient light emission could not be generated on the scintillator plate.
A liquid scintillator method is a method of measuring radiation (in particular, β-rays) emitted from a liquid sample using a liquid scintillator. In this method, a liquid sample containing a radioactive substance is added to the liquid scintillator. In this case, the liquid scintillator exists near the periphery of the radioactive substance, and emits light due to the β-ray emitted from the radioactive substance. In this method, however, a problem occurs in which the spectrum changes due to chemical quenching. In addition, it takes a great effort to treat organic waste solutions generated after the measurement.
Patent Literature 1 discloses application of a hydrophilic treatment on a surface of a plastic scintillator, to adhere the liquid sample thereon. Patent Literature 2 discloses a tritium detection apparatus. In this apparatus, a liquid layer is formed by cooling water vapor containing tritium, and β-rays emitted from the liquid layer are detected. The structure, however, causes the above-described problem of self-absorption.